There are a number of patents that disclose bending machines and linear guides for the bending machines. For example, DE 39 22 326 C2 and EP 0 934 783 B1, respectively, disclose bending machines comprising two articulated robots, each of the robots being displaceable laterally of a gripping unit on a linear guide of a guiding path comprising two stationarily supported guide bars. The displacement is effected via a guide block that is longitudinally displaceable on the guide bars. Feeding is effected via a chain supported in the machine bed. However, the positioning accuracy of the chain drive is rather insufficient and the chain also tends to lengthen. Patent DE 603 01 913 T2 discloses a linear guide, wherein the guide blocks are displaced partially via toothed rack drives. In this case, the toothed rack is securely fixed, over its entire length, to a base body. A drive pinion, mounted to a carriage, rolls on the rack or, a securely mounted drive comprising a pinion moves a toothed rack, which is mounted to the carriage. In both cases, the alignment of the toothed rack guides is complex in the case of longer paths of displacement and can be obtained only with great difficulty due to the tolerances to be complied with. This requires very exact processing of the surfaces.
Further, patent DE 601 14 303 T2 discloses a linear guide for a collet feed in a pipe-bending machine, wherein guide bars are mounted above a plate and toothed racks are mounted below the plate, the toothed racks effecting the feed together with pinions arranged below the toothed racks. In this case, manufacturing, aligning and mounting the toothed rack and the linear guide requires a lot of work which, in addition, has to be carried out several times.
Patent DE 10 2004 008 409 B3, as well as EP 1 380 362 A1, disclose linear guides for a collet feed for pipe-bending machines, wherein a toothed rack, again fixed over its entire length, engages a corresponding driving pinion. This arrangement also requires a relatively large amount of manufacturing, aligning and mounting work associated with the toothed rack and the linear guide, which again has to be carried out several times.
Patent EP 1 366 850 A1 discloses a linear guide using a guide bar to which several toothed rack segments are mounted. When using such a linear guide in a processing machine, vibrations are transmitted from the drive to the guide bar, reducing the useful life of the guide bar quite considerably.
A linear guide of the above-mentioned type is disclosed in EP 0 345 536 B1 and uses guide bars in the form of round rack guides. One of the round rack guides is, at the same time, provided with teeth and serves as a linear guide and feeding element. The round rack guide is mounted over its entire length to a bearing rail, with the teeth being arranged laterally or on top. However, there is a disadvantage here in that round rack guides for longer paths of displacement (e.g. greater than 2 m) are not available.
In view thereof, there is a need to improve a linear guide of the above-mentioned type such that it can also be used, in a functionally reliable manner, for greater lengths of displacement (e.g. greater than 2 m) with particularly little mounting and aligning work.